In certain prior pneumatic systems for operating reversible air motors known to the art complex, relatively large and expensive valves are required to handle reverse flow as it is essential that the air flow on the exhaust side of the motor is not restricted and does not create back pressure on the motor as this detracts from or destroys the torque of the motor. The conventional reversible piston type valves of which I am aware are not suitable for this purpose because of failure to provide unrestricted exhaust flow with no back pressure due to various deficiencies such as inadequate or unrestricted exhaust orifice capacity or lack of positive movement of the piston to the full open position.
The present invention is also applicable to pneumatic systems involving relatively large air cylinders having reversible pistons wherein a small escape hole or vent is provided in the cylinder to provide for the controlled escape of air during the return stroke of the piston. These small holes tend to become clogged with liquid, grease or foreign matter, such that the cylinder operation is adversely affected.